A study of the composition and properties of the ion-association complex of Rhodamine B with silicomolybdic acid, with a view to its analytical application

The composition of the ion-association complex of Rhodamine B with silicomolybdate has been examined by Job's method and spectrophotometric titration. The ratio of Rhodamine B to silicon in the complex is 4 : 1. The same ratio is obtained by analysis of the crystalline complex. The composition of the complex is identical in aqueous medium, an organic solvent (ethanol) and in the crystalline state (C(28)H(30)N(2)O(3))(4)SiMo(12)O(40)). The complex is stable in the organic solvent and has its absorption maximum at 555 nm and a molar absorptivity of 5 x 10(5) 1.mole(-1)cm(-1). The complex can be advantageously used for the determination of silicon.     

Role of protonation and of axial ligands in the reductive dechlorination of alkyl chlorides by vitamin B12 complexes. Reductive cleavage of chloroacetonitrile by Co(I) cobalamins and cobinamides

Cobalt(I) cobalamin and cobinamide are efficient catalysts of the hydrogenolysis of aliphatic chloro compounds. Taking chloroacetonitrile as example, the first requirement for high catalytic efficiency is fulfilled by the high reactivity of the Co(I) complex toward the substrate, leading to the alkylcobalt(III) complex. This is further reduced into the alkylcobalt(II) complex. However, the fact that these two reactions are fast is not enough to ensure an efficient catalysis: in DMF catalysis is very poor, while it is high in water. The experiments carried out in DMF with addition of an acid show that a crucial step in the catalytic process is the proton transfer decomposition of the alkylcobalt(II) complex, leading to the product, and closing the catalytic loop by regeneration of the cobalt(I) complex. Another important feature of these catalytic reactions is the role played by axial ligands present in the solution, particularly those that are produced by the catalytic reaction itself, namely, chloride ions and the counteranion of the added acid. The stronger these ligands, the more negative the potential required for the reduction of the alkylcobalt(III) complex. This amounts to a self-moderation effect: the more efficient catalysis, the slower its second step, i.e., the conversion of the alkylcobalt(III) complex into the alkylcobalt(II).     

有机配合剂稳定高价稀土元素的研究 I.丙二酸水溶液中稳定Pr(IV)的研究

本文通过751G型发光光度计和pHS-2型酸度计, 研究了有机配合剂(Pr(IV)-CH~2(COO)~2^-^2)碱式碳酸盐溶于丙二酸水溶 液中, Pr(IV)在该溶液中的行为和稳定情况。总Pr量用EDTA配位滴定法, 二甲酸橙作指示剂;Pr(IV)分析用碘量法, 并扣除空白。     

Trace adsorptive voltammetric determination of antimony in hair

A very sensitive electrochemical procedure for trace determination of antimony is described. The complex of antimony with p-dimethyl-aminophenyl-fluorone (p-DMPF) is adsorbed on a hanging mercury drop electrode (HMDE), and the reduction current of the accumulated complex is measured by voltammetry. In linear sweep voltammetry, the reduction potential of the complex is more positive than that of the free dye. The peak height of the complex is proportional to the concentration of antimony in the range of 4.0 x 10(-9) to 4.0 x 10(-7) M, the detection limit is 1.0 x 10(-9) M Sb(III) for a 5 min preconcentration time. The relative standard error for the determination of 8.0 x 10(-8) M Sb(III) is 2.9%.     

Study of a mathematical model of metal ion complexes in solvent sublation

Separation of metal ion complex, [(C(12)H(8)N(2))(3)Fe(2+)], with surfactant sodium dodecylphrate (DLS) complex from aqueous phase was carried out by solvent sublation, which obeys first-order kinetics. On the base of the complete transport mechanisms, the Langmuir adsorption, and the ion complex equilibrium in the aqueous phase, a mathematical model for the [(C(12)H(8)N(2))(3)Fe(2+)]-surfactant ion complex is obtained with the aid of the Mathematic 4.0 program, 4th Runge-Kutta method, and the Matlab programs. The effects of many parameters, such as K(a), K(l), K(ow), d(i), V(o), V(w), and Q(a), on solvent sublation are investigated. Furthermore, the simulation showed that the model is substantiated for experiments on the solvent sublation of the complex.     

Synthesis of DNA-sequence-selective hairpin polyamide platinum complexes

Two DNA-sequence-selective hairpin polyamide platinum(II) complexes, containing pyrrole and imidazole heterocyclic rings, have been synthesised by different methods. A six-ring complex, selective for (A/T)GGG(A/T) DNA sequences, was made by using solid-phase synthesis, whilst an eight-ring complex, selective for (A/T)CCTG(A/T) DNA sequences, was made by utilising standard wet chemistry. Solid-phase synthesis resulted in a significantly higher yield, required less purification and is more efficient than the wet synthesis; as such, it is the preferred method for further work. The metal complexes were characterised by (1)H and (195)Pt NMR spectroscopy and ESI mass spectrometry. The two compounds provide a foundation for the synthesis of more complex molecules containing multiple hairpins and/or platinum groups.     

Facile ring opening of iron(III) and iron(II) complexes of meso-amino-octaethylporphyrin by dioxygen

Pyridine solutions of ClFe(III)(meso-NH(2)-OEP) undergo oxidative ring opening when exposed to dioxygen. The high-spin iron(III) complex, ClFe(III)(meso-NH(2)-OEP), has been isolated and characterized by X-ray crystallography. In the solid state, it has a five-coordinate structure typical for high-spin (S = 5/2) iron(III) complex. In chloroform-d solution, ClFe(III)(meso-NH(2)-OEP) displays an (1)H NMR spectrum characteristic of a high-spin, five-coordinate complex and is unreactive toward dioxygen. However, in pyridine-d(5) solution a temperature-dependent equilibrium exists between the high-spin (S = 5/2), six-coordinate complex, [(py)ClFe(III)(meso-NH(2)-OEP)], and the six-coordinate, low spin (S = 1/2 with the less common (d(xz)d(yz))(4)(d(xy))(1) ground state)) complex, [(py)(2)Fe(III)(meso-NH(2)-OEP)](+). Such pyridine solutions are air-sensitive, and the remarkable degradation has been monitored by (1)H NMR spectroscopy. These studies reveal a stepwise conversion of ClFe(III)(meso-NH(2)-OEP) into an open-chain tetrapyrrole complex in which the original amino group and the attached meso carbon atom have been converted into a nitrile group. Additional oxidation at an adjacent meso carbon occurs to produce a ligand that binds iron by three pyrrole nitrogen atoms and the oxygen atom introduced at a meso carbon. This open-chain tetrapyrrole complex itself is sensitive to attack by dioxygen and is converted into a tripyrrole complex that is stable to further oxidation and has been isolated. The process of oxidation of the Fe(III) complex, ClFe(III)(meso-NH(2)-OEP), is compared with that of the iron(II) complex, (py)(2)Fe(II)(meso-NH(2)-OEP); both converge to form identical products.     

Highly stereospecific epimerization of alpha-amino acids: conducted tour mechanism

The highly stereospecific and regiospecific recognition of alpha-amino acids exhibited by a novel Co(III) metal complex embodied in the experimental work (Nature 1999, 401, 254) is rationalized from the energetics and structural characteristics with the use of density functional calculations. The steric repulsion between the chiral center of the receptor [Co(III) complex] and alanine has been a cause for the discrimination of complex stabilities. The energies evaluated for all possible alanine binding modes clearly reveal regiospecificity. Our main emphasis is laid on the base-catalyzed epimerization reaction that drives the stereospecific recognition to near completion. The conducted tour mechanism is found to be the most likely candidate. A similar role by the equivalent Zn(II) complex is found.     

NMR and theoretical study of the cooperative interaction of hydrated proton with dibenzo-24-crown-8

Interaction of hydrated protons (HPs) with dibenzo-24-crown-8 (DBC in nitrobenzene-d(5) was studied by (1)H and (13)C NMR under assistance of ab initio-density functional theory (DFT) quantum calculations. HPs were afforded by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) with 3.5 M excess of H(2)O. The forming of a complex between HP and DBC leads to marked and additive relative shifts of both (1)H and (13)C signals. This was utilized for the estimation of the stabilization constant K of the complex. Its value is at least 10(6) l/mol, which agrees with the result of independent extraction method (log K = 6.3). Using absolute integral intensities of the HP signal in a water-saturated system, it was shown that the form of HP present in the complex must be H(5)O(2)(+), in accord with formerly published structure of the complex in crystalline form. The investigation of the dynamics of exchange between bound and free DBC by transverse relaxation using variably spaced pulses in the Carr-Purcell-Meiboom-Gill (CPMG) sequence or on-resonance rotating-frame relaxation with variable spin-lock field intensity was partly hampered by the fast relaxation of some signals in the complex because of relative immobilization of its internal motions. In order to remove these effects, a pulse sequence dipolar interaction-free transverse relaxation (DIFTRE) for static DIFTRE was devised and the MLEV17 pulse sequence with high intensity of electromagnetic field was used in a separate series of experiments. Using the results of these latter experiments, the correlation time of exchange was established to be about 0.8 ms, which complied with the shape of the spectra. The accompanying ab initio DFT calculations showed that the apparent symmetry of the molecules of both DBC and its complex with H(5)O(2)(+) was probably the result of averaging of energetically close conformations (five for DBC and four for the complex). Both NMR and the calculations show that the basic mode of binding of the ion in the complex is analogous to that found in crystal but the most pronounced conformation is slightly different.     

Synthesis, structural characterization and catalytic activity of a multifunctional enzyme mimetic oxoperoxovanadium(V) complex

The synthesis and structural characterization of a novel oxoperoxovanadium(V) complex [VO(O(2))(PAH)(phen)] containing the ligands 2-phenylacetohydroxamic acid (PAHH) and 1,10-phenanthroline (phen) has been accomplished. The oxoperoxovanadium(V) complex was found to mimic both vanadate-dependent haloperoxidase (VHPO) activity as well as nuclease activity through effective interaction with DNA. The complex is the first example of a structurally characterized stable oxoperoxovanadium(V) complex with a coordinated bi-dentate hydroximate moiety (-CONHO(-)) from 2-phenylacetohydroximate (PAH). The oxoperoxovanadium(V) complex has been used as catalyst for the peroxidative bromination reaction of some unsaturated alcohols (e.g. 4-pentene-1-ol, 1-octene-3-ol and 9-decene-1-ol) in the presence of H(2)O(2) and KBr. The catalytic products have been characterized by GC-MS analysis and spectrophotometric methods. The DNA binding of this complex has been established with CT DNA whereas the DNA cleavage was demonstrated with plasmid DNA. The interactions of the complex with DNA have been monitored by electronic absorption and fluorescence emission spectroscopy. Viscometric measurements suggest that the compound is a DNA intercalator. The nuclease activity of this complex was confirmed by gel electrophoresis studies.     

Investigation of a Cu(II)-poly(gamma-glutamic acid) complex in aqueous solution and its insulin-mimetic activity

The complexation between cupric ions (Cu(II)) and poly(gamma-glutamic acid) (gamma-PGA) in aqueous solutions (pH 3-11) has been studied by UV-visible absorption and electron spin resonance (ESR) techniques. Formation of the Cu(II)-gamma-PGA complex is confirmed by the observation of the blue shift of the absorption band in the visible region, anisotropic line shapes in the ESR spectrum at room temperature, and a computer simulation of the visible absorption spectrum of the complex. The structure of the Cu(II)-gamma-PGA complex, depending on the pH, has been determined. The in vitro insulin-mimetic activity of the Cu(II)-gamma-PGA complex is examined by determining both inhibition of free fatty acid release and glucose uptake in isolated rat adipocytes treated with epinephrine, in which the concentration of the Cu(II)-gamma-PGA complex for 50% inhibition of free fatty acid release is very similar to that of CuSO4. However, it is significantly lower than that of a previously reported insulin-mimetic bis(3-hydroxypicolinato)copper(II), [Cu(3hpic)2], complex.     

Exhaustive oxidation of a nickel dithiolate complex: some mechanistic insights en route to sulfate formation

A study of the step-wise oxidation of a Ni(II) diaminodithiolate complex through the formation of sulfate, the ultimate sulfur oxygenate, is reported. Controlled oxygenations or peroxidations of a neutral, planar, tetracoordinate, low-spin Ni(II) complex of a N(2)S(2)-donor ligand, (N,N'-dimethyl-N-N'-bis(2-mecaptoethyl)-1,3-propanediaminato) nickel(ii) (1), led to a series of sulfur oxygenates that have been isolated and characterized by ESI-MS and single-crystal X-ray diffraction. A monosulfenate complex (2) was detected by ESI-MS as a product of oxidation with one equivalent of H(2)O(2). However, this complex proved too unstable to isolate. Reaction of the dithiolate (1) with two equivalents of H(2)O(2) or one O(2) molecule leads to the formation of a monosulfinate complex (3), which was isolated and fully characterized by crystallography. The oxidation product of the monosulfinate (3) produced with either O(2) or H(2)O(2) is an interesting dimeric complex containing both sulfonate and thiolate ligands (4), this complex was fully characterized by crystallography, details of which were reported earlier by us. A disulfonate complex (7) is produced by reaction of 1 in the presence of O(2) or by reaction with exactly six equivalents of H(2)O(2). This complex was isolated and also fully characterized by crystallography. Possible intermediates in the conversion of the monosulfinate complex (3) to the disulfonate complex (7) include complexes with mixed sulfonate/sulfenate (5) or sulfonate/sulfinate (6) ligands. Complex 5, a four-oxygen adduct of 1, was not detected, but the sulfonate/sulfinate complex (6) was isolated and characterized. The oxidation chemistry of 1 is very different from that reported for other planar cis-N(2)S(2) Ni(ii) complexes including N,N'-dimethyl-N-N'-bis(2-mecaptoethyl)-1,3-ethylenediaminato) nickel(II), (8), and N,N'-bis(mercaptoethyl)-1,5-diazacyclooctane nickel(II). To address the structural aspects of the reactivity differences, the crystal structure of 8 was also determined. A comparison of the structures of planar Ni(II) complexes containing cis-dithiolate ligands, strongly suggests that the differences in reactivity are determined in part by the degree of flexibility that is allowed by the NN' chelate ring.     

Infrared matrix isolation study of the 1:1 molecular complex of OVCl3 with (CH3)2O

The 1:1 complex of OVCl(3) with (CH(3))(2)O has been isolated in argon matrices at 14 K, and characterized by infrared spectroscopy. The complex is relatively strongly bound, with significant shifts to vibrational modes of both the acid and base subunits in the complex. For example, the OC(2) symmetric stretch of (CH(3))(2)O shifted from 925 to 891 cm(-1) upon complex formation, while the VCl(3) antisymmetric stretching mode shifted from 505 to 474 cm(-1). Product identification and band assignments were confirmed by isotopic labeling. Attempts to convert the initial 1:1 complex into secondary intermediates by either thermal or photochemical processes were unsuccessful, suggesting that an active hydrogen atom is a key element in determining the pathway for reactions of OVCl(3).     

Identification of face-to-face inclusion complex formation of cyclodextrin bearing an azobenzene group by electrospray ionization mass spectrometry

The solution-based self-assembly of native and permethylated cyclodextrins (CD) bearing an azobenzene substituent has been studied by electrospray ionization mass spectrometry (ESI-MS). The results revealed that the CD molecules form either a contact or a face-to-face inclusion complex depending on the interaction of their substituents. The mass spectrometric study further demonstrated that the inclusion complex is formed through the interaction between the host CD cavity and the guest-substituent and that a contact complex is formed by hydrogen-bonding of the hydroxyl functions at the rims of the CD molecule. We also found that in order to detect the face-to-face inclusion complex by ESI-MS, the following conditions have to be met: (1) The CD moieties must be permethylated to avoid formation of the contact complex, (2) they must possess a guest-substituent of suitable length, such as an azobenzene moiety, and (3) they must possess an NH(2) or OH group at the substituent terminals for protonation and for detection as cations by ESI-MS. Formation of the inclusion complexes was further confirmed by the synthesis of a capped inclusion dimer and a capped monomer. Collision-induced dissociation (CID) experiments have been carried out for the contact, the host-guest inclusion, and the capped inclusion dimers, and the contact complexes are found to be the most stable among them.     

Mechanism of hydrolysis of azalactones catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime

The hydrolysis of 2-methyl-4-benzyl-5(4H)oxazolone (MBA) in a mixture of water and MeCN has been studied — both the spontaneous reaction and that catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime (1). It has been shown that the complex 1 is an effective catalyst for the hydrolysis of MBA (chymotrypsin does not catalyze MBA hydrolysis). The mechanism of MBA hydrolysis catalyzed by this complex includes the formation of a mixed catalyst—substrate complex in which the MBA is coordinated with the metal ion through the N ³ atom. It is suggested that the oxygen atom of the ionized oxime group in such a complex attacks the imine C ² atom of the MBA intramolecularly; this is the rate-determining stage. The change in the order of hydrolysis with respect to the catalyst from 1 to 1/2 when the concentration of 1 is increased indicates that the complex catalyst exists in aqueous solution in two forms, dimeric and monomeric, which are in equilibrium, and only the monomeric form of the complex is responsible for the catalysis. With an excess of the substrate we observe inhibition of the MBA hydrolysis — possibly an indirect indication of participation in the transition state by a water molecule coordinated in an apical position of the complex, which is displaced by excess substrate.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, Moscow 117813. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 536–546, March, 1992.     

A rapid and sensitive extractive spectrophotometric determination of copper(II) in pharmaceutical and environmental samples using benzildithiosemicarbazone.

Benzildithiosemicarbazone (BDTSC) is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of copper(II). BDTSC reacts with copper(II) in the pH range 1.0-7.0 to form a yellowish complex. Beer's law is obeyed in the concentration range 0.5-0.4 microg cm(-3). The yellowish Cu(II)-BDTSC complex in chloroform shows a maximum absorbance at 380 nm, with molar absorptivity and Sandell's sensitivity values of 1.63 x 10(4) dm3 mol(-1) cm(-1) and 0.00389 microg cm(-2), respectively. A repetition of the method is checked by finding the relative standard deviation (RSD) (n = 10), which is 0.6%. The composition of the Cu(II)-BDTSC complex is established as 1:1 by slope analysis, molar ratio and Asmus' methods. An excellent linearity with a correlation coefficient value of 0.98 is obtained for the Cu(II)-BDTSC complex. The instability constant of the complex calculated from Edmond and Birnbaum's method is 7.70 x 10(-4) and that of Asmus' method is 7.66 x 10(-4), at room temperature. The method is successfully employed for the determination copper(II) in pharmaceutical and environmental samples. The reliability of the method is assured by analyzing the standard alloys (BCS 5g, 10g, 19e, 78, 32a, 207 and 179) and by inter-comparison of experimental values, using an atomic absorption spectrometer.     

Chelate resin-iron(II) complex: Adsorption and desorption of nitrogen monoxide at the dry state

A chelate resin-immobilized iron(II) complex was prepared from iron(II) and poly(styrenecodivinylbenzene) which is functionalized by iminodiacetic acid group. It is activated by drying after having been washed with methanol. The resin complex can rapidly adsorb nitrogen monoxide, and the nitrogen monoxide adsorbed on the complex can be released by the treatment with heat. The adsorption of nitrogen monoxide proceeds through the 1:1 complex formation of the NO molecule with the iron(II) atom, and its complex formation constant was calculated as 8330 atm^?1 at room temperature from Langmuir plots. This value does not depend on the solvents used for washing. The activation of the resin complex by the treatment of washing with methanol is derived by increasing the amount of effective iron(II) ions due to the increase in the surface area. Moreover, this resin complex was revealed to have high complex formation constant with NO and high durability to dioxygen compared with an aqueous solution of ethylenediaminetetraacetato–iron(II) complex, which is the corresponding monomeric absorbent commonly used for nitrogen monoxide.     

Prioritization of charge over geometry in transition state analogues of a dual specificity protein kinase

The direct observation of a transition state analogue (TSA) complex for tyrosine phosphorylation by a signaling kinase has been achieved using (19)F NMR analysis of MEK6 in complex with tetrafluoroaluminate (AlF(4)(-)), ADP, and p38α MAP kinase (acceptor residue: Tyr182). Solvent-induced isotope shifts and chemical shifts for the AlF(4)(-) moiety indicate that two fluorine atoms are coordinated by the two catalytic magnesium ions of the kinase active site, while the two remaining fluorides are liganded by protein residues only. An equivalent, yet distinct, AlF(4)(-) complex involving the alternative acceptor residue in p38α (Thr180) is only observed when the Tyr182 is mutated to phenylalanine. The formation of octahedral AlF(4)(-) species for both acceptor residues, rather than the trigonal bipyramidal AlF(3)(0) previously identified in the only other metal fluoride complex with a protein kinase, shows the requirement of MEK6 for a TSA that is isoelectronic with the migrating phosphoryl group. This requirement has hitherto only been demonstrated for proteins having a single catalytic magnesium ion.     

On an intraparticle complex of cationic nanogel with a stoichiometric amount of bound polyanions

A polyelectrolyte nanogel (PENG) particle consisting of lightly cross-linked terpolymer chains of N-isopropylacrylamide, acrylic acid, and 1-vinylimidazole has positive charges in an aqueous medium at pH 3 due to protonation of the imidazole groups, and thereby forms a polyelectrolyte complex with the linear polyanion, potassium poly(vinyl alcohol) sulfate (KPVS). It has been demonstrated that the hydrodynamic radius (Rh), by dynamic light scattering (DLS), and the radius of gyration (Rg), by static light scattering (SLS), of the complex particles are smallest at approximately 1:1 mixing ratio (rm) of anions to cations, in the absence of simple salts such as KCl (Langmuir 2005, 21, 4830). Here, we aimed to study the nature of the complex formed at rm=1 and examined the complex formation process by electrophoretic light scattering (ELS). It was found that the mobility of the cationic PENG with a stoichiometric amount of bound KPVS anions (i.e., the complex formed at rm=1) is positive but not zero at 25 degrees C. This was also the case when the complex was examined by ELS at 45 degrees C, where DLS and SLS show a temperature-driven collapse of the complex. We thus assumed that (a) electroneutrality is maintained in the complex particle with the aid of counterions, but (b) the complex is highly polarizable, and hence (c) during ELS the KPVS anions would dissociate in part from the complex. This hypothesis was supported by the following results: (i) Mixing complexed and uncomplexed PENG particles at different ratios brings about an increase in Rh and a decrease in the light scattering intensity of the complex at the same time, suggesting a polyelectrolyte exchange reaction. (ii) The same phenomenon is seen when poly(diallyldimethylammonium chloride) (PDDA as a polysalt) is added to the complex dispersion, meaning that the PDDA takes out the KPVS from the complex to form a stable PDDA-KPVS complex. (iii) Upon addition of KCl, the complex undergoes little change in Rh (62-67 nm) at a salt concentration (Cs)0.2 M. (iv) The Rh (78 nm) of the soluble complex at Cs from 0.3 to 0.5 M is larger than that at Cs<0.02 M, suggesting dissociation of the KPVS ions. (v) Complexation between KPVS and PDDA as mentioned in (ii) is facilitated in the presence of 0.01 M KCl.     

A Pyridinol Acyl Cofactor in the Active Site of [Fe]-hydrogenase Evidenced by the Reactivity of Model Complexes

Understanding the complex: The decomposition reaction of a water-soluble complex (see scheme; 1) in H(2) O confirms the existence of a unique bidentate pyridinol cofactor in [Fe]-hydrogenase. This unique moiety is confirmed for the first time by the decomposition of a well-defined model complex containing a pyridinyl methyl acyl ligand.